Not only does define ETL with multiple patterns to multiple tables, but
it also defines the searchability, aggregation, labels along with almost
every aspect of the user interfaces for dashboards, thresholds and graphs.

SPL is based on dividing logs into logical namespaces, parsing them into
tables using icons (which define what type of pattern should be used;

I, personally, consider the use of debuggers, with breakpoints and stepping through individual statements to be very much a waste of time... especially as languages have evolved to have expect/require, and even a drop into a REPL.

It took me by surprise how the mailbox formats had changed, when I switched to Dovecot which is the best IMAP/POP3 mail program, in my opinion. It handles large (enormous) mailboxes with many (hundreds of) users. Caching makes things go fast again.

Here is a simple bash utility, to take all users, and convert all mailboxes & folders.
cd /home
for u in *
do
if [ -d /home/$u/Mail ]; then
echo "User: $u"
cd /home/$u/Mail